Mineral fibers and whiskers have been extolled for many years as a strengthening agent for many types of bodies: polymer, ceramic, metal, cermet, etc. By incorporating such finely-divided structures, there is a reinforcing binding that inhibits deleterious cracking. Various fibers and whiskers have been utilized/proposed, including but not limited to alumina, silicon carbide, boron carbide, etc. The principal fiber/whisker for this application has been silicon carbide. A typical description of the potential benefits is set forth in U.S. Pat. No. 5,162,270 issued to Ownby, et al on Nov. 10, 1992. Any appropriate portion of this patent is incorporated herein by reference. Of course, there are many other references to the use of fibers and whiskers for strengthening structures.
It has been determined, however, that silicon carbide fibers and whiskers, and probably a number of other mineral fibers and whiskers, pose a serious industrial health hazard that is at least as great as the hazard created by asbestos fibers. It is not known why the cell ingests the fiber/whisker, but the problem has been known to exist for many years. The problem apparently does not exist to any extent after a reinforced product has been produced (e.g., it is not primarily a public health problem); rather, the problem occurs during the fabrication and handling of the raw fibers/whiskers and thus is an industrial health hazard. This has resulted in halting the fabrication of mineral fibers/whiskers in most countries, with Japan and the United States being the only countries where limited fabrication continues.
The designation hereinafter of "fiber/whisker" is used to designate both fiber and whisker materials, or only one of the materials. Fibers are generally considered to be polycrystalline materials while whiskers are considered to be single crystal material. The health risk is primarily associated with these fibers and/or whiskers that are sufficiently small to be respirable.
Information describing the toxicity of silicon carbide whiskers is reported in, for example, the following publications. Other typical publications related to this toxicity are cited therein.
"The Toxicity, in Vitro, of Silicon Carbide Whiskers" Gerald L Vaughan, et al, Environmental Research, 56, 57-67 (1991); PA1 "The Immediate Effects of Silicon Carbide Whiskers Upon Tracheal Epithelium" Environmental Research, 56, 178-185 (1991); PA1 "Pulmonary Response, in Vivo, to Silicon Carbide Whiskers", Environmental Research, 63, 191-201 (1993).
Accordingly it is an object of the present invention to provide a mineral fiber/whisker for use in structure strengthening, etc. that has a reduced toxicity toward living mammalian cells.
A further object of the present invention is to produce a hydrophobic mineral fiber/whisker to substantially reduce the potential for interaction between the fiber/whisker and living mammalian cells within the pulmonary airways.
Another object of the present invention is to provide a silicone-type coating upon mineral fibers/whiskers to prevent intimate contact between the fiber/whisker itself and living mammalian cells to substantially reduce toxicity to these cells.
It is also an object of the present invention to provide a silicon carbide fiber/whisker having a coating thereon whereby the resultant fiber/whisker has substantially reduced toxicity to living mammalian cells.
Also, it is an object of the present invention to provide a method for the preparation of a mineral fiber/whisker having the reduced toxicity such that operations can be more safely resumed in preparing such mineral fibers/whiskers for use in strengthening and other applications of these materials.
These and other objects of the present invention will become apparent upon a consideration of the following detailed description of the invention.